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MEIOSIS chapter 11 section 4

MEIOSIS chapter 11 section 4. SC SCIENCE STANDARD B-4.5 Students will demonstrate understanding of characteristics of phases of Meiosis I and II. Meiosis Vocabulary. Homologous : term used to refer to chromosomes that each have corresponding chromosome from opposite-sex parent

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MEIOSIS chapter 11 section 4

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  1. MEIOSISchapter 11 section 4 SC SCIENCE STANDARD B-4.5 Students will demonstrate understanding of characteristics of phases of Meiosis I and II.

  2. Meiosis Vocabulary • Homologous: term used to refer to chromosomes that each have corresponding chromosome from opposite-sex parent • Example: Your # 12 chromosome from your mom is homologous to your # 12 chromosome you received from your dad

  3. Diploid: refers to a cell that contains both sets of homologous chromosomes • Referred to as 2n • 2n in humans = 46

  4. Haploid: refers to cells that have one set of chromosomes • Referred to as n • In humans n = 23

  5. Meiosis Phases • Meiosis is a process of reduction division in which the # of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • Only occurs in sex cells • Involves 2 distinct divisions: • Meiosis I • Meiosis II

  6. Meiosis I • Prior to: • each chromosome has replicated

  7. Meiosis I: Prophase I • Homologous chromosomes are paired forming a tetrad

  8. Prophase I • Chromatids (#4) in tetrad exchange portions with their homologous partner = crossing-over • Results in new combinations of alleles

  9. Meiosis I continued • Metaphase I • Homologous pairs line up on metaphase plate • Anaphase I • Homologous chromosomes separate and move to opposite poles

  10. Meiosis I continued • Telophase I • Same as telophase in mitosis • Cytokinesis I • 2 daughter cells • 1set of duplicated chromosomes (n) • Chromosomes are different from parent cell

  11. Meiosis II • 2 cells made in Meiosis I immediately enter Meiosis II • Except there is no replication of chromosomes prior to Prophase II

  12. Meiosis II • Prophase II • Each chromosome has 2 sister chromatids • No crossing over • Spindles start to form • Nuclear envelope & nucleolus fade away • (a lot like prophase in mitosis)

  13. Meiosis II continued • Metaphase II • Chromosomes line up on metaphase plate • Spindles attach to centromeres • (just like metaphase in mitosis)

  14. Anaphase II • Centromeres split separating sister chromatids • Individual chromosomes move toward poles of cell

  15. Telophase II & Cytokinesis II • Nuclear envelopes and nucleoli reform • Spindle disappears • Cleavage furrow forms • 4 daughter cells formed each with haploid # (n) of chromosomes

  16. Meiosis

  17. Comparing :Mitosis Meiosis • Parent cell produces 2 genetically identical daughter cells • Parent cell produces 4 genetically different daughter cells

  18. Gamete Formation • Males: • Even cell divisions at end of Meiosis I & II • Females: • uneven cell divisions in Meiosis I & II (most of cytoplasm goes to 1 cell)

  19. GametesMales: Females: • Females:

  20. Meiosis Animations • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html • http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html

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